摘要:

The breeding biology and causes of nest failure were examined for Black‐throated DiversGavia arcticain core areas of their Scottish breeding range in 1983–1987. Breeding was confirmed for up to 88% of territorial pairs each year (n= 28–62), and 76% of nests were on islands. Hatching success was consistently low with, on average, only 43% of territorial pairs managing to hatch a clutch each year; 64% of recorded nest failures occurred during the first week of the 4‐week incubation period.Overall breeding success in West Sutherland in 1984–1987 averaged 0.23 chicks per territorial pair per year, while in Ross‐shire for 1986–1987 it was 0.29. Forty percent of hatched chicks survived to fledge, and 92% of recorded deaths occurred in the first fortnight after hatching; 4.8% of fledged broods held two chicks.Causes of nest failure were assessed with the aid of surveillance cameras. Approximately 30% of losses were due to water level changes (mostly floods), 48% to predators (primarily nocturnal mammals, but also Hooded CrowsCorvus corone), 13% to human egg collectors and 5% to desertion following human disturbance.Scottish Black‐throated Divers produce only half the number of chicks tentatively estimated to be required to maintain a stable population. The main difference between the Scottish and more successful Swedish populations is in the degree of

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02822.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

We recorded the age of individual wing and tail feathers of Black‐browed and Grey‐headed AlbatrossesDiomedea melanophrisandD. chrysostomaof known age and breeding status at Bird Island, South Georgia. Breeders and non‐breeders of both species moult their rectrices annually. Non‐breeders moult primaries biennially. In the first year of a cycle, the outer three and some inner primaries are moulted descendantly; in the next year the inner primaries are moulted ascendantly, starting from primary seven. There is a general progression to moulting equal numbers of primaries in each half of the cycle by the time breeding starts at about 10 years of age. Grey‐headed Albatrosses usually moult fewer primaries than Black‐browed Albatrosses, particularly as 3‐year‐olds, when they undertake substantial plumage change in body moult. Most secondaries in Black‐browed Albatrosses have been replaced once by age 4 years. Breeding Black‐browed Albatrosses continue the moult pattern established as immatures whether they fail or not, as do failed Grey‐headed Albatrosses. Successful Grey‐headed Albatrosses, which breed again 16 months later, moult their three innermost primaries after breeding in the remainder of the current year and, after a period when moult is interrupted, renew the remaining primaries the following year. Comparisons between species and between failed and successful birds within species indicate that moult rate is not closely linked to the length of the interval between breeding attempts. Interspecies differences are better explained by breeding latitude, with tropical albatrosses moulting twice as fast as sub‐Antarctic species, possibly reflecting food availability ou

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02823.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The dispersal behaviour of 30 radio‐tagged young Spanish Imperial EaglesAquila adalbertiwas studied in southwestern Spain in 1986–1990. The dispersal process involved first departure from the natal population, exploratory movements, temporary settlements and returns to the natal population. The dispersal process lasted for the whole of the immature period studied, and behaviour was radically different from that displayed by territorial adults. Movements between temporary settling areas and the natal population occurred continually throughout the dispersal period. Return to the natal population could be used by the young to explore the possibilities for pair formation where a vacancy may have occurred in the breeding populat

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02824.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Black and Red KitesMilvus migransandM. milvuschase other raptors approaching their nests. The study of this behaviour during the post‐fledging period suggested that it reflects mainly, but not only, anti‐predator behaviour. The frequency of vigilance and aggressive chases decreased through the post‐fledging period as predicted by theoretical models of nest defence. Although predation risks were similar, Black Kites invested more time chasing intruders than did Red Kites. Black Kites, unlike Red Kites, chased away intruding juveniles, which may be interpreted as a behaviour to avoid investment in unrelated fledglings. Black Kites usually nest in loose colonies where the risk of, and selection pressures against, accidental investment in unrelated fledglings is likely to be greater than for Red Kites. Differences in aggressive chases by Black and Red Kites are better related to this than to different predation

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02825.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The feeding ecology of DotterelCharadrius morinellusadults and chicks was studied on three Scottish breeding areas. On the basis of 2324 prey items identified from 234 faeces, we show that (i) birds feed selectively and (ii) age‐related and seasonal differences in food selection occur.The diet comprised mainly beetles (Coleoptera), sawflies (Symphyta) and the adults and larvae ofTipula montana.The faeces of adult Dotterel contained a high proportion of beetles, whereas chick faeces had more soft‐bodied prey. However, whenT. montanaadults emergeden masse(every second year) both adults and chicks took more tipulids. On one area, larvalT. montanacomprised much of the diet soon after the birds arrived on their breeding grounds and just before leaving in autumn. The preferred feeding habitats were flat or gently slopingRacomitrium lanuginosumorJuncus trifidusheaths or the transition zone between moss heath and montane bog. Dwarf‐shrub, grass‐dominated and single bog communities were avoided. The preferred feeding habitats were those in which pitfall trap catches of the main prey were highest. A close juxtaposition of montane bog andR. lanuginosumheaths met the feeding requirements of both chicks and adults, respectively. Recent changes in the breeding distribution of Dotterel in Britain may be related to de‐ terioration in feeding and breeding habitat due to overgrazing by sheep and greater habitat acid

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02826.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Estimates of the energy budgets of nonbreeding waders (Charadrii) have frequently been hampered by ignorance of the birds' nocturnal activities. During the premigratory period (March), Grey PloversPluvialis squatarolaand WhimbrelsNumenius phaeopusat the Zwartkops estuary, South Africa, foraged throughout the nocturnal as well as the diurnal low‐tide period. Although both species continued to forage visually at night, they exhibited behavioural changes to compensate for the reduced visibility. Both species foraged more slowly at night, taking fewer steps per minute, and Grey Plovers paused for longer to search for prey. Prey items were sighted from shorter distances at night than during the day. Energy intake rates, however, did not differ significantly by day and night for either species, and both achieved over 40% of their daily low‐tide period intake at night. The energy intake rates and total daily intake of Grey Plovers, which fed exclusively on the study area, exceeded allometrically predicted val

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02827.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

A surveillance radar in southwest Iceland was recorded by time‐lapse filming in order to monitor the migration pattern of birds departing from or passing Iceland on their way to high‐arctic breeding grounds in late May and early June 1988–1990. An overwhelming majority of the radar echoes from migrating bird flocks departed from Iceland but a few seemed to pass over from further south. Timing of movements and supplementary field observations indicated that mainly four species were involved, i.e. KnotCalidris canutus, TurnstoneArenaria interpres.SanderlingC. albaand Brent GooseBranta bernicla.Departures in late May from stopover sites in Iceland took place mainly in the afternoons, peaking between 1700 and 1900h in all 3 years. The departure intensity was lowest between 0100 and 1300h. Flight paths were generally straight, and the average track direction was towards the northwest (315°), suggesting that the majority of birds were heading for a transglacial migration across the Greenland icecap on their way to breeding grounds in northwest Greenland and northern Canada. Track directions varied with wind, although to a rather small degree, indicating partial drift or pseudodrift. More echoes were registered in easterly winds (tailwinds) and fewer in northerly winds than expected from random. Airspeeds were significantly slower than groundspeeds (average 17.0 and 18.7 m/s, respectively), showing that the birds more often than not benefited from tail wind assi

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02828.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

We studied Great Reed WarblersAcrocephalus arundinaceusat two localities in Ghana during the winter. In the north (Tono), the birds arrived from late September and conducted a rapid moult soon after arrival. Towards the end of moult, birds accumulated fat and disappeared from the site. In the south (Tafo), birds arrived from mid‐November in fresh plumage. This seemed to be the final wintering area as birds stayed there during the winter. In March‐April they again accumulated fat, although only small amounts, before spring migration back to breeding ar

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02829.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Aquatic WarblersAcrocephalus paludicolawere studied in a natural fen mire in the Biebrza River valley, the main breeding ground of the species in its entire distribution range. The number of males present and singing at the sample plot changed considerably during the breeding season. Individual identified colour‐ringed males sang with unchanged intensity throughout the breeding season. The period of daily singing activity differed from other species ofAcrocephalus; males sang at dusk rather than at dawn. Males took no part in rearing nestlings but remained on territory and showed vigilance behaviour. The density of males in the breeding season ranged from 1.0 to 10.9 per 10 ha. The density of nesting females ranged from 1.3 to 15.7 per 10 ha. In the most suitable habitat females were more numerous than males. The distribution of females (nests) was clumped where potential food resources were higher. Nests were well hidden in places with deeper water between sedge tufts and an abundance of old dry sedge. Females feeding nestlings collected most food within a 5–60‐m radius (mean 31.7 m). The return rate of males was higher than that of females. The results suggest a mating system that is intermediate between facultative polygyny and promis

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02830.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The Seychelles WarblerAcrocephalus sechellensisis a resident, cooperative breeder in a saturated, island environment, whose song structure diners significantly from European marshlandAcrocephalusspecies. The song is transmitted within a more restricted frequency range, that which propagates most effectively through tropical forest. The Seychelles Warbler has developed a relatively short, simple song, used for territorial defence throughout the year, which is readily elicited by playback. Yet it also has a complex repertoire of song types, and song activity peaks before and declines during breeding, suggesting a sexual function. The demands of tropical island life are thus reflected in both the structure and function of song in the Seychelles Warbler.

ISSN:0019-1019    

DOI:10.1111/j.1474-919X.1993.tb02831.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY